Skyrmion Alignment and Pinning Effects in a Disordered Multi-Phase Skyrmion Material Co8Zn8Mn4

Abstract

Underlying disorder in skyrmion materials may both inhibit and facilitate skyrmion reorientations and changes in topology. The identification of these disorder-induced topologically active regimes is critical to realizing robust skyrmion spintronic implementations, yet few studies exist for disordered bulk samples. Here, we employ small-angle neutron scattering (SANS) and micromagnetic simulations to examine the influence of skyrmion order on skyrmion lattice formation, transition, and reorientation dynamics across the phase space of a disordered polycrystalline Co${}_8$Zn${}_8$Mn${}_4$ bulk sample. Our measurements reveal a new disordered-to-ordered skyrmion square lattice transition pathway characterized by the novel promotion of four-fold order in SANS and accompanied by a change in topology of the system, reinforced through micromagnetic simulations. Pinning responses are observed to dominate skyrmion dynamics in the metastable triangular lattice phase, enhancing skyrmion stabilization through a remarkable and previously undetected skyrmion memory effect which reproduces previous ordering processes and persists in zero field. These results uncover the cooperative interplay of anisotropy and disorder in skyrmion formation and restructuring dynamics, establishing new tunable pathways for skyrmion manipulation.

arXiv comment15 pages, 11 figures, Version 2 showing micromagnetic simulations that reinforce a new disordered-to-ordered square lattice skyrmion transition pathway which entails a change in topological charge. SANS simulations are included which estimate the change in the skyrmion lattice and ferromagnetic volume fractions from the metastable triangular lattice skyrmion phase to the skyrmion memory phase

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